Field of the Invention
The present invention generally relates to methods for making golf balls and golf ball components using three-dimensional (3D) additive manufacturing systems. Preferably, a continuous liquid interface printing method is used to make the three-dimensional structure. More preferably, this method is used to make a three-dimensional inner core. An outer core made of rubber or other material may be disposed about the inner core. A single or multi-layered cover may encapsulate the core assembly to form the finished golf ball. The outer core and cover layers also may be made using methods of this invention. This invention further encompasses golf balls and golf ball components made by such methods.
Brief Review of the Related Art
Multi-piece, solid golf balls having a solid inner core protected by a cover are used today by recreational and professional golfers. The golf balls may have single-layered or multi-layered cores. Normally, the core layers are made of a highly resilient natural or synthetic rubber material such as styrene butadiene, polybutadiene, polyisoprene, or ethylene acid copolymer ionomers. The covers may be single or multi-layered and made of a durable material such as ethylene acid copolymer ionomers or polyurethanes. Also, there may be intermediate (casing) layers disposed between the core and cover. Manufacturers of golf balls use different ball constructions to impart specific properties and features to the balls.
The core is the primary source of resiliency for the golf ball and is often referred to as the “engine” of the ball. The resiliency or coefficient of restitution (“COR”) of a golf ball (or golf ball component, particularly a core) means the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize the COR under these conditions. Balls (or cores) with a high rebound velocity have a relatively high COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distances as opposed to balls with lower COR values. Ball resiliency and COR properties are particularly important for long distance shots. For example, balls having high resiliency and COR values tend to travel a far distance when struck by a driver club from a tee. The spin rate of the ball also is an important property. Balls having a relatively high spin rate are particularly desirable for relatively short distance shots made with irons and wedge clubs. Professional and highly skilled amateur golfers can place a back-spin on such balls more easily. By placing the right amount of spin and touch on the ball, the golfer has better control over shot accuracy and placement. This is particularly important for approach shots near the green and helps improve scoring.
Over the years, golf ball manufacturers have looked at adjusting the density or specific gravity among the multiple layers of the golf ball to control its spin rate. In general, the total weight of a golf ball needs to conform to weight limits set by the United States Golf Association (“USGA”). Although the total weight of the golf ball is mandated, the distribution of weight within the ball can vary. Redistributing the weight or mass of the golf ball either towards the center of the ball or towards the outer surface of the ball changes its flight and spin properties.
For example, the weight can be shifted towards the center of the ball to increase the spin rate of the ball as described in Yamada, U.S. Pat. No. 4,625,964. In the '964 patent, a polybutadiene rubber composition is used to form the core. According to the '964 patent, the inner core has a specific gravity of at least 1.50 in order to make the spin rate of the ball comparable to wound balls. The ball further includes a cover an intermediate layer disposed between the core and cover, wherein the intermediate layer has a lower specific gravity than the core. Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a three-piece golf ball containing a two-piece solid rubber core and a cover. The inner core has a diameter in the range of 15-25 mm, a weight of 2-14 grams, a specific gravity of 1.2 to 4.0, and a hardness of 55-80 JISC. The specific gravity of the outer core layer is less than the specific gravity of the inner core by 0.1 to 3.0.
In another example, the inner core structure has a non-uniform thickness and/or contains projecting members. These extending members on the outer surface of the core may be arranged in any suitable geometric pattern. For example, the extending members may be arranged in a grid or lattice; or a series of rows and raised columns. These extending members may be in the form of ridges, bumps, nubs, hooks, juts, ribs, segments, brambles, ribs, spines projections, points, protrusions, and the like. Suitable projecting members and various designs, patterns, and outlays of the members are disclosed in Sullivan et al., U.S. Pat. Nos. 8,137,216 and 8,033,933; Morgan et al., U.S. Pat. No. 7,901,301; Sullivan et al., U.S. Pat. Nos. 7,022,034 and 6,773,364; and Boehm, U.S. Pat. No. 6,293,877,
It would be desirable to have new manufacturing methods for making three-dimensional components for golf balls such as, for example, cores, intermediate (casing) layers, and cover layers. In recent years, three-dimensional additive manufacturing systems have been used to make objects and parts in a wide variety of industries including, for example, apparel, footwear, automotive, aerospace, architecture, construction, packaging, military, jewelry, art, and dental and medical industries.
In general, additive manufacturing refers to systems that use three-dimensional (3D) digital data from an object to build-up the object by depositing metal, plastic, or other material layer-by-layer as opposed to subtractive systems used to build-up the object by removing material (for example, machining/milling an object from a solid block of polymer material). In these systems, computer software is used to collect digital data on the shape and appearance of a real object. A digital model is created and a series of digital cross-sectional slices of the model are taken.
For example, in a three-dimensional (3D) printing system, each slice is reconstructed by depositing a layer of the material and then solidifying it. The digital information is sent to the three-dimensional printer that successively adds thin layers of material (for example, a powder), until the object is produced. The layers are joined together in various ways, and different materials, for example, metal, plastic, ceramic, or glass). For example, in a three-dimensional (3D) printing process, an inkjet printer head can spray a thin layer of liquid plastic onto a build tray. The liquid layer is cured and it solidifies by irradiating it with ultraviolet (UV) light. The build tray is lowered by a layer, and the process is repeated until the model is completely built. In another 3D printing process, powder is used as the printing medium. The powder is spread as a thin layer on the build tray, and then it is solidified with a liquid binder. In Fusion Deposit Modeling (FDM), the nozzles trace the cross-section pattern for each particular layer. An extrusion head deposits a thin layer of the molten thermoplastic material onto a platform. The molten material hardens prior to application of the next layer. In Multi-Jet Modeling (MJM), a printing head that can move in multiple directions (x, y, and z coordinates) includes multiple small jets that apply the thermoplastic material to a platform layer-by-layer, and the material solidifies. In selective laser sintering (SLS), small powder particles are deposited in the desired pattern and then a laser is used to fuse the powder particles together. Other systems include laminate object manufacturing (LOM) and rapid prototyping. In stereolithography (SLA), liquid resin is applied to an elevator platform. The object is built layer-by-layer. For each layer, a laser beam traces a cross-section pattern of the object on the surface of the liquid resin. After the pattern has been traced, the elevator platform descends by the appropriate distance and the process is repeated. The platform is re-coated with liquid resin, and another pattern is traced. In this way, the layers are joined together and the object is built layer-by-layer. After the object is built, it is cleaned of any excess resin by immersing it in a chemical bath and the object is subsequently cured in an ultraviolet oven.
Although some three-dimensional (3D) printing systems may be somewhat effective in producing some 3D parts, there are some drawbacks with such systems. For example, 3D ink-jet printing systems build the part in discrete and separate layers. These ink-jet printed parts commonly exhibit orthotropic or anisotropic mechanical behavior depending on the orientation of the part during fabrication. Also, these 3D ink-jet printing systems can have relatively slow speeds and require support or base structures to build the part.
Thus, there is a need to new manufacturing methods for making golf balls and three-dimensional components for golf balls such as, for example, cores, intermediate (casing) layers, and cover layers. The new method should have a speed advantage over 3D ink-jet printing systems and be capable of producing high quality golf balls and components. The present invention provides such methods having these advantages as well as other benefits along with the resulting golf ball components and finished golf balls.